Images in plain text and the terminal; bounded build parallelism (from dev 16f82cc887af)

- @image under txt and ansi is a picture in characters, in five styles
  (Image_txt_style: halfblock the default, shade, ascii, quadrant,
  braille), sized to the terminal's width less a margin when ktext runs
  in one, every cell in its own colours under ansi; a figure's caption
  is centred under it and no txt caption is ruled off any more.
- The build compiles as many files at once as the machine has cores
  (JOBS; make -C com JOBS=1 for a small machine): the sub-makes' bare -j
  meant unlimited parallelism and exhausted 8 GB machines. The three
  install pages say "make -C com".

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

sks/Makefile

@@ -35,15 +35,15 @@ all : support $(SO_DIRS)
 support : $(SUPPORT_DIRS)
 
 kutil :
-	$(MAKE) -j -C $(KS)/kutil
+	$(MAKE) -j$(JOBS) -C $(KS)/kutil
 
 target : kutil
-	$(MAKE) -j -C $(KS)/target
+	$(MAKE) -j$(JOBS) -C $(KS)/target
 
 # Pattern rule for the DSO directories
 # Each depends on the library and support directories
 $(SO_DIRS) : support $(LIBRARY)
-	$(MAKE) -j -C $(KS)/$@
+	$(MAKE) -j$(JOBS) -C $(KS)/$@
 
 # Clean all subdirectories
 clean :